Bump Newtonsoft.Json from 12.0.3 to 13.0.2 in /test/ProjNet.Tests (#110)

Bumps [Newtonsoft.Json](https://github.com/JamesNK/Newtonsoft.Json) from 12.0.3 to 13.0.2.
- [Release notes](https://github.com/JamesNK/Newtonsoft.Json/releases)
- [Commits](JamesNK/Newtonsoft.Json@12.0.3...13.0.2)

---
updated-dependencies:
- dependency-name: Newtonsoft.Json
  dependency-type: direct:production
...

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test/ProjNet.Tests/ProjNET.Tests.csproj

@@ -8,7 +8,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
+    <PackageReference Include="Newtonsoft.Json" Version="13.0.2" />
     <PackageReference Include="Npgsql" Version="4.1.3.1" />
   </ItemGroup>